1、子Activity组件在进程内的启动过程

       在Android Activity组件的启动过程http://blog.csdn.net/jltxgcy/article/details/35984557一文中，我们已经详细分析了Activity的启动过程，对于子Activity组件在进程内的启动过程，我们只分析它们之间的不同。

       主要是2处，1是不需要创建新的任务栈，2是不需要创建新进程和子线程。

       第1点，体现在如下代码上：

       ～/Android/frameworks/base/services/java/com/android/server/am

       ----ActivityStack.java

public class ActivityStack {

	......

	final int startActivityUncheckedLocked(ActivityRecord r,
		   ActivityRecord sourceRecord, Uri[] grantedUriPermissions,
		   int grantedMode, boolean onlyIfNeeded, boolean doResume) {
		final Intent intent = r.intent;
		final int callingUid = r.launchedFromUid;

		int launchFlags = intent.getFlags();

		......

		if (sourceRecord == null) {
		   ......
		} else if (sourceRecord.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) {
		   ......
		} else if (r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE
		   ......
		}

		if (r.resultTo != null && (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
		   ......
		}

		boolean addingToTask = false;
		........

		boolean newTask = false;

		// Should this be considered a new task?
		if (r.resultTo == null && !addingToTask
		   && (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) {
			......

		} else if (sourceRecord != null) {
			......
			// An existing activity is starting this new activity, so we want
			// to keep the new one in the same task as the one that is starting
			// it.
			r.task = sourceRecord.task;
			......

		} else {
		   ......
		}

		......

		startActivityLocked(r, newTask, doResume);
		return START_SUCCESS;
	}

	......

}

 private final void startSpecificActivityLocked(ActivityRecord r,
            boolean andResume, boolean checkConfig) {
        // Is this activity's application already running?
        ProcessRecord app = mService.getProcessRecordLocked(r.processName,
                r.info.applicationInfo.uid);
        
        .....
        
        if (app != null && app.thread != null) {
            try {
                realStartActivityLocked(r, app, andResume, checkConfig);
                return;
            } catch (RemoteException e) {
                .....
            }

            .....
        }

        ......
}

      和Android Activity组件的启动过程http://blog.csdn.net/jltxgcy/article/details/35984557一文中，主要有一个区别，不需要创建新的任务栈。代码如上面所示。还需要创建新进程和子线程。